Electric control



Nov. 14, 1944. c. J. LUNDBORG ELECTRIC CONTROL 2 Sheets-Sheet 1 INVENTOR 1 10771507 ATTORNEYS Filed Jan. 21, 1942 C. J. LUNDBORG Nov. 14, 1944.

ELECTRI C CONTROL Filed Jan. 21, 1942 2 Sheets-Sheet 2 HQ it MKWM a 5 3 Mn T N NW VR E o W a .1. M Z

- wherein the power absorbed by Patented Nov. 14, 1944 UNITED STATES PATENT OFFICE- ELECTRIC CONTROL Carl J. Lundborg, Great Falls, Mont. Application January 21, 1942, Serial No. 427,567

4 Claims.

This invention relates to electric control circuits, and, more particularly, to electric control circuits involving control of the output grid control rectifiers. The invention is particularly applicable to control of the total load imposed by a plurality of independent loads upon a common source of electric power.

Numerous operations involving the use of electric apparatus call for a control device which will effect a desired variation in the operation of the electric apparatus. For exmple, in the operation of a plant using electric power for various purposes such as for electrolytic cells, a rolling mill, tram system, etc... it is frequently desirableto maintain the total power used in the plant at a substantially constant value. This may be accomplished it means are provided for controlling the power absorbed by one of the loads so as to maintain the total power consumed at a predetermined desired value or rate, particularly when the power is paid for on the basis of a peak load rate. In a plant such as that referred to above such units as the rolling mill, tram system, etc., is a variable yet cannot be controlled at will because of the demanding nature of these loads, the electrolytic cells represent a load which may be economically varied substantially at' will and in such manner that the total amount; 01 power consumed by all loads in the plant remains substantially constant at the peak load value, or at Thepresent invention any other desired value. provides a control circuit capable of thus maintaining a substantially constant power consumption in such a plant, particularly by control of the power absorbed by the electrolytic cells, although the invention is applicable to many other operations in which control of the combined output of a plurality of grid control rectifiers may be utilized for control of electric apparatus.

The control circuit of my invention for regulating the combined output of a plurality of grid control rectifiers comprises a plurality of grid control rectifiers interconnected to combine the output of the individual rectiflers, means for provid ing the grids of the rectifiers with a. potential having a predetermined phase relationship with the potential of the plates of the rectifiers, and means including relay means for controlling or regulating the phase relationship between the grid and plate potentials of at least one of the rectiflers in such manner as to control the combined output of the interconnected rectifiers. The phase relationship between the grid and plate potentials of the rectifiers is advantageously such as to ob.

" the resistor of potentiometer R: to

the vacuum tube VT:.

tain a substantially intermediate output froxii'each of the rectifiers, and the phase relationship between the grid and plate potentials or at least one of the rectiflers is regulated by a variable super. posed potential responsive to the variation is an electric apparatus which it is desired to control.

Theseand other companying drawings, in which Fig. 1 is a circuit diagram of an apparatus embodying the invention;

Fig. 2 shows one form 01' may be used in the circuit and contact assembly that Fig. 3 is a circuit diagram showing one appli."

circuit of my inventio'nto control of the power absorption in an illustrative figure being drawn as a cation of the control for the operation of the three thermionic tubes VT1, VT: and VT; and the circuits appurtenant thereto. The tube VT1 comprises a full wave rectifying tube connected across a secondary of the transformer T2. The direct potential output of the tube VT1, which is filtered through the circuit including the choke coil I I and the condensers C1 and C2, is connected across the resistance R1 which serves as a voltage divider. The positive side of the voltage divider R1 is connected through the plate of The negative side of the voltage divider R1 is connected through the variable resistance R: and the photoelectric cell PTl to the grid of the tube VTz. The cathode of the tube VT: is connected to the voltage divider R1 at a point positive with respect to the negative side or the voltage divider, and the cathode and grid of the tube VT: are interconnected through a condenser C3. The grid of the tube VT: is also connected through the photoelectric tube PT: and

the variable resistance R4 to a point on the voltage divider R1 which is positive with respect to the point on R1 to which the cathode of the tube VT: is connected. Thus, the photoelectric cell PT1 is in a circuit which connects the grid of the tube VT: to a source of negative potential and the photoelectric cell PT: is in a-circuit which connects the grid of the tube VT: to a source oi positive potential.

In the operation of this portion of the control features of the invention will be more fully understood by reference to the ac-i illustrated in Fig. 1;

circuit, light falling with equal distribution from a source hereinafter described, upon the photoelectric cells P'Ti and PT: permits current to flow in the two circuits including the photoelectric cell P'Ir and the resistance R: and including the photoelectric cell PTz and the resistance R4, respectively, thus tending to balance the negative and positive potentials imposed on the grid of the tube VT: controlled by these two circuits. Under these conditions current will flow through the tube VTz. When, however, the distribution of light intensity on the two photoelectric cells is such that more light falls upon PT: than on PIi, the conductivity of the photoelectric cell PT: is greater than that of the cell PT; and consequently a less negative potential is imposed on the grid of the tube VTz. this change in light distribution between the two photoelectric cells is reflected by the change in grid potential in the tube VT: is controlled, with any given capacity for the condenser C3, by the values of the variable resistances R: and R4. By the proper selection of the values of the resistances R: and R4, any rapid oscillation or fluctuation in the light distribution between the two photoelectric cells is substantially completely damped and does not result in a corresponding oscillation of the grid potential of the tube VTe. This is true of both types of relay means here disclosed, viz., the photoelectric cell type of Fig. 1, and the mechanical type of Fig. 2, later to be described. As the potential of the grid of the tube VT: becomes more positive the current flow ing through this tube increases. An increase in the negative bias of the grid of the tube VTa, resulting from more light falling on the photoelectric cell P'I1 than on the cell P'Iz, decreases the tube current flowing through the tube VTz.

The vacuum tube VT: acts as an electronic valve. The grid of the tube VT: is connected to the voltage divider R1 at a point negative with respect to the positive end of the voltage divider. The center tap of the cathode of the tube VT: is connected to the sliding contact of the potentiometer R2. Accordingly, the bias voltage on the grid of tube VT3 is the difference between the voltage drop on the voltage divider R1 from its positive end to the point at which the grid of VT: is connected and the voltage drop in the potentiometer R2 between the positive end of voltage divider R1 and the sliding contact of the potentiometer. By adjusting the position of the sliding contacton the potentiometer to give a, negative bias to the grid of VT: when the tube current of VT: is normal, an increase in the tube current of VT2 will produce a greater voltage drop in the potentiometer R2, thus decreasing the negative grid bias in the tube VTs. With a decrease in the negative bias on the grid of the tube VTa, the tube current flowing through the tube VT: increases. Thus, with more light falling on the photoelectric cell P'Iz than on the cell PT1, the tube current through VTz increases and the tube current through VTz also increases, whereas a reversal of this light distribution causes a decrease in the tube currents of both VTz and VT].

The grid control rectifier circuit providing the The speed with which controlled power output for the desired regulation of an electric apparatus includes two gas-filled grid control rectifiers, or Thyratrons, l2 and [3. The filaments of the rectifiers are supplied from a filament transformer T3 connected across one-half of the secondary of the transformer T1. The plates of the rectifiers l2 and I3 are connected across the ends of the transformer T1 secondary. An auxiliary circuit comprising the condenser C4 and the primary of the transformer T4 is connected between the plate of the rectifier l3 and the center tap of the transformer T1 secondary. The grid ll of the rectifier l3 and the grid ii of the rectifier I! are connected across the ends of the secondary winding of the transformer T4. The auxiliary circuit causes a potential to be impressed on the grids I4 and I! having a definite phase relationship with the plate potentials of the rectincrs l3 and I2, respectively. The magnitude of the grid current of the rectifiers is limited by the resistance Ra connected between the center tap of the transformer T4 secondary and the cathodes of both rectiflers. The plate of the vacuum tube VT: is connected to the same end of the transformer T1 secondary as is the plate of the rectifier l2, and the cathode of the tube VT: is connected to the auxiliary circuit at a point common to the condenser C4 and the end of the primary of transformer T4 remote from the end connected to the center tap on transformer T1, completing the plate circuit of tube VTs. Thus, the variable plate current flowing through the vacuum tube VT: and entering the auxiliary circuit between the condenser C4 and the primary of the transformer T4, acting as a variable superposed potential substantially out of phase with the grid potentials of the rectifiers l2 and I3, alters the phase relationship between the grid and plate potentials of the rectifiers l2 and i3 (and also modifies the effective amplitudes of the grid potentials). These changes in phase relationship effect corresponding changes in unidirectional output current from rectifiers I2 and I3. The output current from the interconnected rectiflers l2 and I3 is obtained through line It comprising connections to the center tap of the transformer Ti secondary and to the center taps of the interconnected cathodes of these rectiflers.

This embodiment of the invention may be applied, as shown in Fig. 3, to the maintenance of the power consumption of a plant including an electrolytic cell tank room. Fig. 3 being drawn as a continuation of Fig. 1, terminals 34 and 35, respectively, of both figures being identical. The various independent power consuming loads may comprise rolling mills, smelters, tram systems, compressors, and the like, and are represented in Fig. 3 by loads #1, #2 and #3 connected across the power line H. To simplify the diagram this power line is shown as comprising but two wires, but a multi-phase line is usually employed in such plants. Variations in the power absorbed by these loads are automatically compensated by control, in accordance with the present invention, of the power consumed by the electrolytic cell tanks l8. The power transformer 20 is connected to the power line 11 and through terminals 3! to the primary of transformer '1, of Fig. 1, and supplies'to the primary of the transformer T1 power necessary for the operation of the control circuit shown in Fig. 1. Also connected to the power line l1 are the motors 2| of the motor-generator exciters A, B and C and the motors 22 of the plurality of motor-generator sets which supply direct current power to the electrolytic cell tanks l8. The field excitation for the motors 22 and generators 23 of these motor-generator sets is provided by the generators 24 of the motor-generator exciters A, B and C.

The power meter M (shown generally) is connected in known manner to the power line H in either the vided with a divided mirror 25, is connected to the power line in such manner that a drop in the plant power consumption below the desired rate of power consumption causes the light from a suitable light source 26 to be reflected from the mirror 25 with greater intensity on the photoelectric cell PTz than on the cell PT1 01' the control circuit illustrated in Fig. 1. This causes an increase in tube current through the vacuum tube V'I'z, and a corresponding increasein the output of the interconnected rectifiers l2 and I! through lines IS. The output of nected rectifiers Iland 13 in lines l6,"as shown in Figs. 1 and 3, is con nected to the double throw switch 21;

portion of either of the field rheostats ZBa'and 2 of the motor-generator used heretofore. When the variable resistances the interconthrough terminals 35 exciters A and B, respectively. The current output of the interconnected rectifiers l2 and i3 is supplied to field rheostat 28:: or 28b in such manner that an increase in output current increases the total current flowing through the shunt field of either of the generators 24 of exciters Aand B thus tending to increase the output of I these I ta exciters, which in turn increases the ou'tput of generators 23. thus increasing the load on motors 22 and therefore on power line I 1. 3 It will be noted that the output through lines l6 rheostat acting field circuit of each exciter.

primarily a connection in the However, this is interest of con.-

in the shunt field circuit of either exciter A or Y B. The control circuit supplying the current is advantageously under normal conlight distribution The output from the generator 24 of the mo' tor-generator exciter A is connected through its series field, the circuit breaker 30a and the switch 3m to the bus supplying excitation to the fields of the generators 23. The output from the generator 24 of the motor-generator exciter B is connected through its series field and the circuit breaker 30b to a double-throw switch 3Ib which a is adapted to supply the output of exciter 8 either to the bus for the fields of the generators 23 or to the bus for the fields of the motors 22; The output from the generator 24 of exciter C is connected through the circuit breaker 30c and the switch Me to the bus for the fields of the motors 22. Thus, complete flexibility is afforded for utilizing the controlled current output from the control circuit in varying the power output from the generators 23 to the electrolytic cell tanks i8 by means of variations in the field excitation of generators or motors of the motorgenerator sets. Uniformity in operation and output of the exciters A, B and C is enhanced by PT1 and PTz) the- 1 toelectric cell's PTi constants to the Ca, there is substantially no hunting and the Where photoelectric. cells are used as the equalizing connection between each of the exciter generators 24 comprising the line 32 and the equalizer switches 33. Inasmuch as the power output of the generators 28 tothe electrolytic cell tanks IBrepresents converted power obtained from the power line l1, variations in the power suppliedto the electrolytic cell tanks represent variations in, the power consumed by this load on the power line.-

The control circuit of my invention has'many advantages over 'control circuits proposed or R1 and R4 are adjusted to give the proper time circuit including the condenser tubes. The accuracy and sensitivityjoij the control circuit are to some extent dependent upon the relay System used totranslate tqj the rest of the control circuit the electrlcal ariation to be controlled.

, photoelectric cells, thus giving. a proportional step control; The phoand -PTz.may be so illuminated that only one or the. other of these cells is illurelay such as-thatshownvinFig. 2

as a fixed resistance in the shunt minated when the meter reading is either above or below its normalposition. Where a contact is used in' The range of the control circuit (regar dless of the type of relay used)' is readily adjusted to meet any conditions by tentiometer R2 which determines the vmagnitude of the grid bias of the tube VT3.

The control circuit of the invention may be used in any electric system wherein control of the system may be efiected by a variable direct current comprising the output of the interconnected rectifiers. For example; the control circuit may be used to effect voltage regulation of an A. C. or D. C. generator, or for supplying part or all of the field excitation of a D. C. motor, or for supplying all or part of both field and armature current of a D. C. motor as a means of speed and torque control of the motor. The control circuit may also be used to regulate current in an A. C. circuit by supplying the direct current output of the control circuit to a DC. winding of a saturarect current, within the current capacity of the rectifier tubes, may be utilized,

tion is not disturbedwby subsequent changes in I the. operating constants of the regulation of the poerator connected to tor-generator exciter the electrolytic cells, a mohaving the motor connected to said power source and the generator connected to the motor-generator set in such manner as to influence the output of the motorgenerator set to the electrolytic cells, a control element adapted to respond to a variation in the total power absorbed by said independent loads, the motor-generator set and the motor-generator exciter, and a control circuit comprising a plurality of gasfilled grid control rectifiers interconnected to combine the outputs of the individual rectifiers, the combined output of said rectifiers being connected to the motor-generator exciter in such manner as to influence the output of the exciter, means for providing the grids of the rectifiers with a potential having a predetermined phase relationship with the potential or the plates of the rectifiers, and means responsive to said control element for controlling the phase relationship between the grid and plate potentials of at least one of the rectifiers in such manner as to control the combined output'oi the interconnected rectifiers and hence the output of the motor-generator set to the electrolytic cells so as to maintain the power absorbed by all of the loads at a substantially constant value.

2. A plant adapted to consume electric power at a substantially constant rate, comprising, a source of alternating electric power, an independent load subject to wide variation in power consumption connectible to said source, a dependent load of a type capable of absorbing power economically over a wide range of rates and including at least one electrolytic cell, a motorgenerator set of which the motor is connected to said source and the output of the generator is connected to supply said dependent load, said motor-generator set including a field winding, a control element connected to respond to variations in the total power consumed by said plant, a control circuit including a plurality of gas-filled rectifiers having control-gridv and plate electrodes, said plate electrodes being interconnected to combine the outputs of the individual rectifiers, means responsive to the combined output of said rectifiers to control the current in said field winding, means impressing on the grids and plates of said rectifiers alternating potentials having a predetermined phase relation, and means responsive to said control element for varying the phase relation of the grid and plate potentials of said rectifiers in accordance with said variations in power consumed by said independent load and in such manner that the rate of power consumption by said plant remains substantially constant.

3-. A plant adapted to consume electric power at a substantially constant rate, comprising, a source of alternating electric power, and independent load subject to variation in sumption connectible to said source, a dependent load of a type capable of absorbing electric power economically over a range of rates, a motorgenerator set of which the motor is connected to said source and the electric output of the generator is connected to supply said dependent load, regulating means associated with said motor-generator set for controlling the output of said generator, a control element connected to respond to variations in the total power consumed by said plant, a control circuit including at least one gas-filled rectifier tube having control-grid and plate electrodes, means responsive to the outpower conput of said rectifier to control said regulating means, means impressing on the grid and plate electrodes of said rectifier tube alternating potentials having a predetermined phase relation, and means responsive to said control element for varying the phase relation of said grid and plate potentials in accordance with said variation in power consumed bysaid independent load and in such manner that the rate or power consumption by said plant remains substantially constant.

4. In a power control system, an alternatingcurrent power source, a load, a rectifier coupled to said source and having. an output circuit, a first resistor connected in said output circuit so that output current from said rectifier fiows therethrough, a first vacuum tube having a cathode, a grid, a plate and a plate circuit between said cathode and plate, said plate circuit including a portion of said resistor and a second resistor connected in series, two-photoelectric cells each having two electrodes, a connection from said cathode to a point on said first resistor, a common connection from one electrode 01' each of said photoelectric cells to the grid oi said vacuum tube, and connections from each of the other electrodes of said photoelectric cells to different points on said first resistor which are negative and positive, respectively, with respect to the point of connection of the cathode of said vacuum tube on said first resistor, whereby actuation of said photoelectric cells tend to impress on said grid a resultant control potential in accordance with the relative actuation oi! said pho toelectric cells, means including adjustable means connected to said vacuum tube for determining the response of said vacuum tube to the actuation of said photoelectric cells, a second vacuum tube having a cathode, a grid, and a plate, a connection from the grid of said second vacuum tube to a point on said first resistor and a connection from the cathode thereof to a point on said second resistor, a first transformer having a secondary provided with an intermediate tap, two gas-filled grid control rectifiers having their plates connected across said secondary, said secondary being coupled to said power source, load control means responsive to changes in output current from said rectifiers for modifying the power consumption on said source, the cathodes of said rectifiers being connected through said load control means to said intermediate tap, an auxiliary circuit including a condenser and the primary of a second transformer connected between the plate of one or said rectifiers and said tap, the plate of the other of said rectifiers being connected to the plate 0! said second vacuum tube, a connection from the cathode of said second vacuum tube to said auxiliary circuit at a point common to said condenser and one end of the primary of said second transformer, the grids of said two rectifiers being connected across the secondary of said second transformer, and a connection from a center tap on said last named secondary to the cathodes of said rectifiers, whereby variation in plate current or said second vacuum tube controls the phase relation between the plate and grid potentials of said rectifiers, a control element connected to respond to load variations on said power source, and light means controllable by said element for actuating said photoelectric cells.

CARL J. LUNDBORG. 

